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Models shared by the SO3D.xyz community. Open any of them in the generator to see exactly how it was built, remix it, or print it as-is. Browse the model library by category

Preview of Buffon's-needle pi tray
By Krypto
Complexity
Medium
MAIN PURPOSE: Estimate pi by dropping matchsticks on a tray of parallel lines
In 1777 the Comte de Buffon found a way to work out pi with nothing but sticks: drop sticks as long as the gap between parallel lines, and the chance that one lands across a line is exactly 2 divided by pi. Drop 40 mm sticks onto this tray, which has raised lines exactly 40 mm apart, count how many you dropped (N) and how many cross or touch a line (C), and pi is about 2N divided by C. A hundred drops gets close to 3.1; a whole class pooling results gets closer still.
AR view Open in app
Preview of Zhang Heng earthquake ball
By Krypto
Complexity
Medium
MAIN PURPOSE: Detect a tremor when a marble balanced on a slender column falls into the dish
In 132 AD the Chinese astronomer Zhang Heng built the first seismoscope: eight bronze dragons each held a ball, and a tremor made one drop its ball into the mouth of a bronze toad, clanging the alarm and showing the direction of the quake. This is the one-dragon version. A marble sits in a shallow cup on top of a tall, slim screw-in column; a door slam, heavy footsteps or a real tremor tips it off and it lands in the dish with a clatter. Place it on different floors and see which part of the house shakes most.
AR view Open in app
Preview of Woodlouse choice chamber
By Krypto
Complexity
Medium
MAIN PURPOSE: Let woodlice choose between damp, dry, light and dark, and count where they go
A classic biology experiment. The four bays meet at an open centre: DAMP and DARK, DAMP and LIGHT, DRY and DARK, DRY and LIGHT. Release ten woodlice in the middle, cover the top with cling film, shade the DARK half with card and wait ten minutes. Almost all of them end up in the damp, dark bay, because woodlice are crustaceans that dry out quickly and hide from the light that would show them to birds. Count them, swap the conditions round and try again, then return them to where you found them.
AR view Open in app
Preview of Ames-room illusion box
By Krypto
Complexity
Simple
MAIN PURPOSE: Make two identical toys look like a giant and a dwarf through a peephole
Look through the peephole and the room looks like an ordinary box, but it is not: the back wall runs at a slant, so the left corner is twice as far away as the right. Put two identical figures in the back corners and one looks like a giant and the other like a dwarf. Move a figure along the back wall and it grows or shrinks before your eyes. It is the Ames room, invented in 1946 and used in films to make actors look tiny next to wizards.
AR view Open in app
Preview of Cloud-chamber cosmic-ray base
By Krypto
Complexity
Simple
MAIN PURPOSE: See the trails of cosmic-ray particles in a home-made cloud chamber
Invisible particles from space pass through you every second, and this lets you see them. Put a slab of dry ice in the base, lay a 3 mm aluminium plate painted matt black on the ledge, and turn a clear plastic tub upside down on the plate with a strip of felt soaked in 99% isopropyl alcohol stuck inside its top. After ten minutes, turn off the lights and shine a torch in from the side: thin white trails appear and vanish as muons, alpha and beta particles streak through the alcohol mist, just as in the chambers that won Nobel prizes.
AR view Open in app
Preview of Phone-screen photoelastic viewer
By Krypto
Complexity
Simple
MAIN PURPOSE: See the hidden stress in clear plastic as rainbows using a phone screen
Your phone screen gives out polarised light, which is half of a stress lab. Lay the phone in the bottom showing a white page, slide a piece of clear plastic in through the slot (a protractor, a CD case, a plastic fork) and put polariser film on the ledge above. Look down and the plastic lights up in rainbow bands wherever it is strained. Squeeze the fork and watch the colours race. Engineers use exactly this, called photoelasticity, to find weak spots in parts.
AR view Open in app
Preview of Moon-crater impact tray
By Krypto
Complexity
Medium
MAIN PURPOSE: Drop pebbles into flour and cocoa from marked heights to make lunar craters
How did the Moon get its craters? Fill the tray with 3 cm of flour, dust cocoa over the top, and drop a marble from the 10 cm mark on the back board, then from the 20 cm mark. Each impact punches out a crater and throws white flour across the dark cocoa in bright rays, just like the rays round the crater Tycho. Compare sizes, heights and weights, then smooth it over and start again.
AR view Open in app
Preview of Stream-table river maker
By Krypto
Complexity
Medium
MAIN PURPOSE: Watch water carve rivers, meanders and a delta in a tray of sand
A geography lesson that builds itself. Fill the tray with damp sand, pour water into the tall cup at the mountain end, and it seeps out through a small hole at the bottom to carve a river down the slope. Watch it meander, cut banks, braid into channels and drop a fan-shaped delta where it reaches the SEA end, where a drain hole lets the water out. Change the slope with a book under the cup and see how a steep river behaves differently from a gentle one.
AR view Open in app
Preview of UV-bead sunscreen tester
By Krypto
Complexity
Medium
MAIN PURPOSE: Prove a sunscreen still works with beads that change colour in sunlight
Is last summer's sunscreen still any good? Fill both dishes with UV colour-change beads, stretch cling film over each, and rub a little sunscreen onto the film over the SPF dish. Put them in the sun: the BARE beads turn bright purple and pink in seconds, while the protected beads stay pale if the sunscreen is working. Try different brands, factors and old bottles, or wipe some off to see why you need to reapply.
AR view Open in app
Preview of Gummy-bear osmosis lab
By Krypto
Complexity
Medium
MAIN PURPOSE: Watch gummy bears grow, shrink or dissolve in four liquids overnight
Put one gummy bear on the millimetre grid in each bay and measure it, then cover them with plain water, salty water, sugary water and vinegar. By morning the water bear has swollen to twice its size as water rushes in through its skin by osmosis, the salty and sugary ones barely change, and the vinegar bear has started to dissolve. Measure them on the grid again and record the results. A classic science experiment in a neat tray.
AR view Open in app

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